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Objective—To evaluate the possible effect of melatonin implants on blood glutathione peroxidase (GSHPx) activity and in the prevention of selenium (Se)-responsive disorders in sheep from an Se-deficient region.

Design—Randomized controlled clinical trial.

Animals—100 Merino ewes.

Procedures—Ewes of the same age, parity, body weight, body condition, and reproductive and health history were randomly allotted to 1 of 2 groups (control and implanted) of 50 sheep each. Treatment consisted of implants of melatonin (18 g) administered SC in the pinna of the right ear 6 weeks prior to introduction of rams. The control group did not receive implants. Hematologic and serum biochemical analyses were performed at various points before and after treatment, in addition to determinations of erythrocyte mean corpuscular fragility (MCF) and blood GSHPx activity. The incidence of Se-responsive disorders in lambs was recorded in both groups.

Results—Hematologic and serum biochemical analyses yielded values within respective reference ranges for both groups. Significant differences between groups were evident in MCF at early mating (lower in the implanted group vs the control group) and in blood GSHPx activity at early mating, gestation, and early lambing (higher in the implanted group vs the control group). There were significantly fewer lambs with nutritional myodystrophy in the implanted versus the control group.

Conclusions and Clinical Relevance—Use of melatonin implants in sheep may improve reproductive performance and yield an earlier start of breeding season. The stimulating effect of melatonin on GSHPx activity may protect against oxidative damage during the first stage of gestation.

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in American Journal of Veterinary Research